Measurement reporting in a telecommunication system

ABSTRACT

The present invention relates to defining triggers or threshold values for radio signal parameters that are used for determining whether or not to send a measurement report separately for the uplink and downlink direction. The triggers for the uplink and downlink are logically combined so that a measurement report may be sent when measurements in both the uplink and downlink satisfy the triggers, when either measurement does, or when only one of the uplink or downlink measurement does. Preferably, the measurement report is a mobile evaluated handover measurement report triggering a handover. It is preferably triggered in the mobile station when at least one upper threshold of the radio signal parameters for a mobile evaluated handover is exceeded or a lower threshold is gone under.

CROSS REFERENCE TO RELATED APPLICATION:

This application claims priority to Finnish Patent Application SerialNo. 980358, filed on Feb. 17, 1998, through PCT InternationalApplication No. PCT/FI99/00095, filed on Feb. 9, 1999.

FIELD OF THE INVENTION

This invention concerns reporting of measurements on radio interface ina telecommunication system.

BACKGROUND OF THE INVENTION

In mobile telecommunication systems mobile stations MS can use theservices provided by the network using radio connections. The radioconnection uses the channels of called radio interface between themobile station and a base station of the mobile telecommunicationnetwork. Only a limited bandwidth on the radio spectrum is allocated tobe used by the telecommunication systems. To gain capacity enough, thechannels must be used again as densely as possible. To achieve this, thecoverage area of the system is divided into cells, each cell beingserved by one base station. Due to this, the mobile telecommunicationsystems are often also called cellular systems.

The network elements and the internal relation between the networkelements of a mobile telecommunication system are presented in FIG. 1.The network presented in the figure is in accordance with the UMTSsystem currently being standardized by ETSI (European TelecommunicationsStandards Institute). The network comprises base stations BTS (BaseTransceiver Station), that can establish connections with the mobilestations MS, Radio Network Controllers RNC controlling the usage of basestations and Mobile Switching Centers MSC controlling the RNC's. Inaddition, the network comprises a Network Management System NMS, withthe help of which the operator can modify the parameters of the othernetwork elements. The interface between the MSC and the RNC's isgenerally called the lu interface. The interface between the RNC's andthe BTS's is the lubis interface and the interface between the BTS andthe MS's the radio interface. According to some proposals, an interfacelur between the RNC's is specified.

The calls of a mobile station are routed from the BTS via the RNC to theMSC. MSC switches the calls to other mobile switching centers or to thefixed network. The calls can as well be routed to another mobile stationunder the same MSC, or possibly even under the same BTS.

The radio interface between the base stations and the mobile stationsmay be divided into channels using a plurality of divisions. Knownmethods of division are, for example, Time Division Multiplexing TDM,Frequency Division Multiplexing FDM and Code Division Multiplex CDM. InTDM systems, the spectrum allocated for the system is divided intosuccessive time frames consisting of time slots, each time slot definingone channel. In FDM the channel is defined by the frequency used in theconnection. In CDM the channel is defined by the spreading code used inthe connection. These methods can be used separately or be combined.

To be able to successfully communicate with the mobiletelecommunications network, the mobile station continuously monitors theradio signals sent by the base stations. In the idle mode the mobilesdecode the strongest signal received, and when needed request theestablishment of a connection from the base station transmitting thissignal.

During an active connection, the connection can be moved from one basestation to another. The connection can be moved from one base station toanother by simply rerouting the signal, which is called hard handover.The system interference can be decreased and thus the capacity increasedespecially in CDMA (Code Division Multiple Access) systems utilizing CDMby using soft handovers in which the mobile has simultaneouslyconnections with a plurality of base stations, these base stationsforming the so called active set of the connection.

The handover may be

-   -   intra-cell handovers    -   inter-cell handovers between two base stations under the same        radio network controller    -   inter-RNC handovers between two RNC's under the same MSC, or    -   inter MSC handover between two cells under different MSC's.

In addition, the handover can be divided into intra-frequency handoversin which all the channels involved in the handover procedure are on thesame frequency and inter-frequency handovers, in which there arechannels from at least two frequencies involved in the handoverprocedure.

To be able to establish the handovers to right base stations during anactive connection, the mobile station continuously measures the radiosignals from the base stations it is in connection with as well as theirneighboring base stations. The measurement results are transmitted tothe network using the measurement reporting scheme specified in thesystem. Based on the reports, the network initiates the handover whenthe mobile station would have a better or at least sufficiently goodradio connection to another base station.

In addition to the network initiated handovers, also mobile evaluatedhandovers are known. In an exemplary description of a mobile evaluatedhandover, the mobile station monitors the signal levels received fromneighboring base stations and reports to the network those beaconsignals which are above or below a given set of thresholds. Thosethresholds can be dynamically adjusted as will be explained in thefollowing. Based on this reporting scheme, the network will decidewhether the active set of the connection is to be changed.

Two type of thresholds are used: the first one to report beacons withsufficient power to be used for coherent demodulation, and the secondone to report beacons whose power has declined to a level where it isnot beneficial to be used for receiving the sent information. Based onthis information, the network orders the MS to add or remove basestation signals from its active set.

While soft handover improves overall performance it may in somesituations negatively impact system capacity and network resources. Thisis due to the unnecessary branches between the MS and the base stationsin the active set. On the downlink direction from the base stations tothe mobile station, excessive branch reduces system capacity while onthe uplink direction from the mobile station to the base stations, itcosts more network resources.

To solve this problem, the principle of dynamic thresholds for activeset management is known in prior art. In this method, the MS detectsbeacons crossing a given static threshold T1. When crossing thisthreshold the beacon is moved to a candidate set. It is then searchedmore frequently and tested against a second dynamic threshold T2. Thissecond threshold T2 will test if the beacon is worth adding to theactive set.

When the beacons corresponding to the branches in the active set areweak, adding an additional branch signal, even a poor one, will improveperformance. In these situations, a relatively low value of T2 is used.When there is one or more dominant beacons, adding an additional weakerbranch whose beacon signal is above T1 will not improve performance butwill utilize more network resources. In these situations a higher valueof T2 is used.

After detecting a base station signal above T2, the MS will report itback to the network. The network will then set up the handover resourcesand order the MS to coherently demodulate the signal of this additionalbranch.

Beacons can be dropped from the active set according to the sameprinciples. When the beacon strength decreases below a dynamic thresholdT3, the handover connection is removed, and the beacon is moved back tothe candidate set. The threshold T3 is a function of the total energy ofbeacons in the active set. When beacons in the active set are weak,removal a branch, even a weak one, will decrease performance. In thesesituations, a relatively low value of T3 is used. When there is one ormore dominant branches, removal of a weaker signal will not decreaseperformance but will make the utilization of the network resources moreefficient. In these situations a higher value of T3 is used. Branchesnot contributing sufficiently to the total received energy will bedropped. When further decreasing below a static threshold T4 a beacon isremoved from the candidate set.

To be able to control the connection, the network needs in differentsituations different kinds and different amount of measurementinformation. The more information is sent the more efficient thehandover algorithm are. However, the more information the mobile stationsends the network, the more radio resources are spent. Thus, themeasurement reporting schemes according to prior art are alwayscompromises between the efficiency of the handover algorithms and theusage of radio resources.

WO9802010 relates to a process and a device in a radio communicationsystem for observing the quality of channels that are to be used inuplink and channels that are to be used in downlink. A qualityparameter, for example the interference, is measured for both uplinkchannels and downlink channels from a measurement receiver comprised ineach base station. The measured interference is an approximation to thereal downlink interference. The approximation has best correspondencewith the real interference situation when the base station and themobile stations are placed at similar height, for instance in micro- andpico cells. The measurement values can be used for adaptive allocationof frequencies or channels, or for giving statistical information aboutthe radio communication system.

As the usage of mobile telecommunication systems and multimediaapplications requiring large bandwidths is growing, the present methodsare no longer sufficient, thus limiting the performance of the mobiletelecommunication networks. The objective of the present invention is aflexible measurement reporting scheme which solves this problem.

SUMMARY OF THE INVENTION

The basic idea of this invention is to define triggers, e.g. thresholdvalues for radio signal parameters, for sending a measurement reportseparately for downlink and uplink directions. In addition, it isspecified how the outputs of these triggers are to be combined. Forexample, it may be determined whether the measurement report is to besent, for example, when both the uplink and downlink conditions are met,when either of them is met, based entirely on the uplink conditions orbased entirely on the downlink conditions.

The measurement report types is preferably a mobile evaluated handovermeasurement report triggering a handover. Such a report is triggered inthe mobile station when at least one upper threshold of the radio signalparameters for a mobile evaluated handover is exceeded or lowerthreshold gone under.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described more closely with reference to theaccompanying schematic drawings, in which

FIG. 1 shows a mobile telecommunication system;

FIG. 2 shows the structure of a MEHO algorithm;

FIGS. 3, 4, 5, 6 and 7 each show a decision flow chart, and

FIG. 8 shows functional entities in a mobile station.

DETAILED DESCRIPTION OF THE INVENTION

In the following, preferred embodiments of the invention are studiesfurther.

In this context mobile evaluated handover means, that a handovermeasurement algorithm situated in the mobile triggers the handoverreport. The actual HO decision is always performed by the network. Thehandover report types can be further divided into intra-frequency andinter-frequency handover report types.

The Intra-Frequency Handover

The algorithm presented in the following includes the possibility to useinformation about the downlink (DL), uplink (UL) or both as the triggerfor the HO report. Also this scheme provides a flexible means to controlthe information content of the HO report. The actual thresholds andtimers in the algorithm are selected to be such, that a wide variety ofHO algorithms can be constructed by the appropriate setting of these.

The mobile station continuously performs measurements on the radiosignals from different BTS's according to the procedure described in thefollowing.

The mobile determines the received power of the beacon channel for BTSi.This power is denoted as Prx,i (mW). The MS performs this measurementfor time period t (a parameter set by network). The value of P_(rx,i) isaveraged over the measurement period. The result of this operation isdenoted as P_(—)ave_(rx,i). When the measurement is completed, the pathloss estimate, denoted as Li (dB), is calculated as: $\begin{matrix}{L_{i} = {{- 10}\;\log_{10}\;{\left( \frac{{P\_ ave}_{{rx},i}}{{P\_ beacon}_{{tx},i}} \right).}}} & (1)\end{matrix}$

In (1), the unit of P_(—)beacon_(tx,i) is mW.

During the same measurement period t the MS also estimates theinterference power of the beacon channel before or after (this ispreferably a parameter defined by the network) correlating the receivedsum signal with the spreading code. The values calculated before orafter the correlation differ due to the fact that the correlationremarkably reduces the interference caused by other connections. Thisinterference is denoted as I_(i) (mW). The interference is also averagedover the measurement period. After the averaging has been performed, theaverage value is converted into dBm. This average is denoted asI_(—)ave_(i).

The MS is also to receive, e.g. on the beacon channel, the DL_(—)offsetvalue of BTS_(i), denoted as DL_(—)offset_(i) (dB), which is arelatively stable parameter and there is thus no need to re-receive itfor each measurement period. The purpose of this base station specificparameter is to specify for different cell sizes. The mobiles are handedover from a first set of cells more willingly than from a second set ofcells. These cells of the first set thus become smaller than the cellsof the other set. The offset value can be seen as an additional basestation specific part of the threshold values that are soon to bepresented more closely.

From the above information the MS is to calculate one DL HO measurementS_(dl,i) sample asS _(dl,i) =L _(i) +I _(ave,i) +DL _(—) offset _(i)  (2)

It is to be noted that the larger the value of S_(dl,I), the worse thelink from the base station to the mobile station is. The scope of thisinvention is not limited to the use of this particular measure, butother measures of the link quality may as well be used when implementingthe present invention. As one example, the bit error ratio BER in thereceived radio signal can be used as the measure.

The MS is also to receive, e.g. on the beacon channel, the totalinterference power, I_(ul,i) (dBm) at the BTS_(i) and the UL offsetvalue, UL_(—)offset_(i) (dB) of BTS_(i). The MS is then to calculate thevalue of one UL HO measurement sample asS _(ul,i) =L _(i) +I _(ul,i) +UL _(—) offset _(i)  (3)

When these measurements and calculations have been performed for BTS_(i)the MS is then to place the results as the first elements in the vectorsL_(—)vect_(i) (for the value of L_(i)), S_(—)vect_(dl,i) (for the valueof S_(dl,i)) and S_(—)vect_(ul,i) (for the value of S_(ul,i)). The lastelement of these vectors is discarded. The vectors comprise the historyof the measurement results. The length of the history maintained,defined by the length n of these vectors is a network parameter.

Having performed the measurements for this base station signal the MSchecks whether a MEHO (Mobile Evaluated HandOver) report is to betransmitted according to the HO algorithm described in the following.The argument of the algorithm may be for instance either median or meanof the vectors S_(—)vect_(dl,i) and S_(—)vect_(ul,i), and is preferabledefined by the network. In addition, the MS starts to measure the beaconsignal transmitted by the next BTS BTS_(i+1).

The HO algorithm is used to trigger the transmission of the MEHOmeasurement report. In the algorithm the UL and DL directions oftransmission are treated separately. So actually two algorithms canfunction in the MS independently. The network can command the MS to useeither one of them or both for the triggering of measurement reporttransmission. It should be noted, however, that the active set is alwaysthe same for both directions of transfer.

The algorithm includes the below thresholds:

-   -   1. Branch addition threshold denoted in this document as        BA_(—)abs_(th) and BA_(—)rel_(th),    -   2. Branch deletion threshold denoted in this document as        BD_(—)abs_(th) and BD_(—)rel_(th), and    -   3. Branch replacement threshold denoted in this document as        BR_(—)rel_(th)

For the thresholds 1 and 2, both an absolute and a relative thresholdare defined. Separate values can be defined for the uplink and thedownlink directions. The thresholds are used in Branch Addition (BA),the Branch Deletion (BD) and the Branch Replacement (BR) decision units.These units may be implemented as hardware units, software blocks or acombination of these.

The basic structure of these algorithms is presented in FIG. 2. Theuplink comparison unit ULU compares the measurement results of theuplink radio signals to triggers defined by the thresholds set to thesesignals, and outputs a logical truth value. The downlink comparison unitDLU compares the measurement results of the downlink radio signals totriggers defined by the thresholds set to these signals, and outputs alogical truth value. The results of ULU and DLU are combined to onelogical signal using a logical function. The logical value may be, forexample, AND or OR function, or a function outputting directly one ofthe input values of the block. The truth value of this signal isverified, and a report is sent if the truth value is TRUE, for example.Of course, using a different logical function when combining the outputsof ULU and DLU, it can be defined that the report is sent if the truthvalue is FALSE.

The parallel decision units BA, BD and BR shown in FIG. 2 are used indifferent situations. BA is used when the base station is not in theactive set of the connection, and the number of links between the MS andBTS's in the active set is less than a given limit N_(AS,max). The valueof N_(AS,max) is a preferably a parameter set by the network.

BD is used when the base station is in the active set of the connection.To prevent ping-pong effect, the logical functions of the BA and BDblocks must be consistent so that the same measurement values for a linkbetween the MS and a BTS may not cause both the units to trigger ameasurement report suggesting an addition or deletion of the same link.For example, if logical functions AND and OR are used, the value OR maynot be used in both the decision blocks.

BR is used when the base station is not in the active set of theconnection and the number of links between the MS and BTS's in theactive set is equal to the limit N_(AS,max). This decision unit is usedto replace on link of the active set by another one having better radiocharacteristics.

One algorithmic implementation of the downlink comparison unit DLU ofthe branch addition algorithm BA is shown in FIG. 3. The algorithm isused for beacon signals from base stations that do not belong to theactive set. At stage A1 it is checked whether the number of basestations in the active set is less than a predefined limit, i.e. whetherthe active set is full. As an example, the limit 3 can be used here. Ifthe active set is full, the branch replacement algorithm is selectedinstead of this algorithm (stage A10).

If the active set is not full the procedure proceeds to stage A2, A3 andA4, in which

-   -   it is checked whether new measurement results have been received        (stage A2),    -   S_(i,DL) is compared to absolute threshold BA_(—)abs_(th, DL),        and    -   S^(i,DL) is compared to threshold        S_(—)best_(i,DL)+BA_(—)rel_(th,DL), in which S_(—)best_(i,DL) id        the value measured for the best active branch.

If new results have been received and both the threshold valuesBA_(—)abs_(th,DL) and S_(—)best_(i,DL)+BA_(—)rel_(th,DL) are higher thanS_(i,DL), the output of the DLU is set to TRUE.

The uplink branch can be implemented using a similar algorithm. If newresults for the uplink have been received and both the threshold valuesBA_(—)abs_(th,UL) and S_(—)best_(i,UL)+BA_(—)rel_(th,UL) are higher thanS_(i,UL), the output of the ULU is set to TRUE. The threshold valuesBA_(—)abs_(th,DL)/BA_(—)abs_(th,UL) andBA_(—)rel_(th,DL)/BA_(—)rel_(th,UL) used in different directions may bedifferent from each other or identical.

The values of the DLU and ULU algorithms are inputted into the logicalfunction, as shown in FIG. 2. MEHO measurement report is sent if thefunction outputs a value TRUE. For example, if the logical value used isAND, the MEHO measurement report is sent when both the ULU and DLU havevalue TRUE.

An algorithmic implementation of the downlink comparison unit DLU of thebranch deletion algorithm BD is shown in FIG. 4. This algorithm is usedfor beacon signals from base stations that belong to the active set.

It is first checked whether new measurement results have been received(stage D2). The measurement result S_(i,DL) is compared to thresholdsBD_(—)abs_(th,UL) (stage D3) and S_(—)best_(i,DL)+BD_(—)rel_(th,UL)(stage D4). If either of these thresholds is lower than S_(i,DL), theDLU is set to TRUE (stage D5). Otherwise, DLU is set to FALSE (stageD10) and the next beacon signal in the active set is measured.

A similar comparison in made between the uplink measurement results anduplink thresholds to define the value of ULU. DLU and ULU are combinedusing a logical function defined by the network to make a decisionwhether to send or not to send a MEHO measurement report. To prevent theping-pong effect, the logical function used is selected so that the samemeasurement results never cause the BA to request the addition of abranch and the BD to delete the same branch. To meet this requirement,only one of the logical functions used in BA and BD algorithms accordingto the same reporting option may be a logical OR function. This isdepicted in the following table for two different options formeasurement reporting:

Logical function for BA Logical function for BD Option 1 AND OR Option 2OR AND Option 3 AND AND

An algorithmic implementation of the downlink comparison unit DLU of thebranch replacement algorithm BR is shown in FIG. 5. The algorithm isused for beacon signals from base stations that do not belong to theactive set. At stage R1 it is checked whether the number of basestations in the active set is equal a predefined limit, i.e. whether theactive set is full. As an example, the limit 3 can be used here. If theactive set is not full, the branch addition algorithm is selectedinstead of this algorithm (stage R10).

If the active set is full the procedure proceeds to stage in which it ischecked whether new measurement results have been received (stage R2).If no new measurement results have been received, the next beacon signalis studied. If new measurement result S_(i,DL) has been received it iscompared at stage R3 to the measurement value S_(—)worst_(i,DL) of theworst link in the active set. If S_(—)worst_(i,DL) exceeds S_(i,DL) witha margin of BR_(—)rel_(th) DLU is set to TRUE (stage R4). Otherwise ULUis set to FALSE (stage R20) and the measurements on a next BTS notbelonging to the active set studied.

The uplink branch can be implemented using a similar algorithm. In thiscomparison, S_(i,UL) is compared to S_(—)worst_(i,DL) of the worst linkin the active set. If S_(i,DL) exceeds S_(—)worst_(i,DL) with a marginof BR_(—)rel_(th) DLU is set to TRUE. The margin values BR_(—)rel_(th)are preferably identical in downlink and uplink directions, but alsodifferent values in different directions can be used. This is aparameter that is defined by the network. DLU and ULU are combined usinga logical function to make a decision whether to send or not to send anMEHO measurement report. The logical function is preferably an logicalAND function. In another preferred embodiment, the logical function canbe adjusted freely by the network. The output of the logical functioncan be, e.g. the truth value of DLU or ULU.

When the MEHO algorithms in the mobile station trigger the measurementreport the status of the M best cells/sectors is transmitted. Thetransmitted measurement report is always to include the appropriatevalues for the active set. The M best cells/sectors are determined byusing the values of S_(i,dl) or S_(i,ul) depending on whether it was DLor UL algorithm that triggered the report. The contents of the report ispreferably determined with an message sent from the network. Themeasurement report includes, e.g. the following values for eachcelVsector to be reported. These values are the filtered values.

-   -   1. S_(i,dl)    -   2. S_(i,ul)    -   3. L_(i)

It should be noted, that the measurement report can include informationonly about neighbour BTSs whose beacon signals have been decoded. Thusthe handover report has to include the information of the number of BTSsthat are being reported.

Also the information included in the measurement report may preferablybe defined by the network. For example, the number of beacon signalswhose power level is to be reported in a measurement report ispreferably defined by the network.

The Inter-Frequency HO

The inter-frequency measurements are always initiated by the network.Thus the mobile can perform inter-frequency MEHO only after the networkhas first commanded the MS to start the inter-frequency HO measurements.

There are at least three different reasons for inter-frequency HO:

-   -   1. Coverage. The MS is e.g. exiting the coverage area of a        microcell and has to hand over to a macrocell. This case may be        relatively simple. For example if the branch deletion has        triggered a measurement report and only one branch is active the        conclusion by the network is, that the MS is exiting the        coverage area. The network responds to this by transmitting a        message ‘start i-f measurements’. This message includes the        possible candidate BTSs. The mobile would then start searching        for a stronger BTS on the other frequency. The transmission of        the measurement report is triggered when the MS finds a        candidate BTS on the other (new) frequency that is stronger than        the best active branch on the current frequency.    -   2. Load. If for some reason the load on the used frequency is        higher than on some other available frequency an inter-frequency        HO may be appropriate. This situation would probably be known        only by the network. After the network has detected the overload        situation the actions are the same as in case 1    -   3. Mobile speed. The speed of the MS is so high, that an        excessive amount of handovers are needed if the MS is connected        to the microcell layer. This is an item for further study. The        most crucial question is the detection of the MS speed. That is,        there a method to reliably estimate the MS speed? Can the        received beacon powers be measured often enough to be able to        use fast fading based methods? What signalling does the MS use        to indicate its' speed if the estimation is in the mobile?

After the MS has been commanded by the network to start theinter-frequency measurements the MS is to perform the measurements onthe frequency given in the start measurement command.

The algorithm is used to trigger the transmission of the inter-frequencymeasurement report. In the algorithm the UL and DL directions oftransmission are treated separately. So, actually two decisionalgorithms, DLU and ULU function in the MS independently. The outputs ofthese algorithms are combined as shown in FIG. 2 to make the finaldecision concerning sending the measurement report. The network cancommand the MS to use either one of them or both for the triggering ofmeasurement report transmission. It should however be noted, that theactive set is always the same for both directions of transfer.

The algorithm includes the below threshold. For the threshold anabsolute and a relative threshold CF_(—)abs_(th) and CF_(—)rel_(th) aredefined. The decision flow chart for DLU unit of the algorithm is shownin FIG. 7.

If new measurement results have been acquired in the new frequency notbelonging to the active set, the link losses the beacon signal issuffering are compared to an absolute threshold CF_(—)abs_(th). If thequality of the link is sufficient it is compared to the best link in theactive set. If the quality is better with a predetermined margin theoutput of the DLU algorithm is set to TRUE.

A similar algorithm ULU is run for downlink direction. The outputs ofDLU and ULU are combined using a logical function as described earlier.

When the HO algorithms trigger the inter-frequency measurement reportthe status of the M best cells/sectors is transmitted. The M bestcells/sectors are determined by using the values of S_(i,dl) or S_(i,ul)depending on whether it was DL or UL algorithm that triggered thereport. The contents of the report is determined with a message sentfrom the network. The measurement report includes, e.g. the followingvalues for each cell/sector to be reported. These values are thefiltered values.

-   -   1. S_(i,dl)    -   2. S_(i,ul)    -   3. L_(i)

It must be noted that the possible logical functions are not limited tothose presented in the examples above. For instance, if the outputs ofthe DLU and ULU functions are not binary but have more levels or areeven continuous functions triggered by some events on the radio signalsin respective directions, fuzzy logical functions can be used whenmaking the decision whether to send or not to send a measurement reportbased on the outputs of the functions DLU and ULU. The fuzzy logicalfunctions are preferably given by the network.

A mobile station according the invention is shown in FIG. 8. As itscharacteristics, the mobile station has

-   -   receiving means for receiving information about first and second        set of trigger conditions corresponding, respectively, to uplink        and downlink signals and a logical function,    -   monitoring means for monitoring the radio signals,    -   checking means which is responsive to the receiving means and        the monitoring means and which has the functionality of checking        the state of each trigger conditions,    -   combining means responsive to the checking means for combining        the states according to the logical function, and    -   sending means responsive to the combining means for sending a        measurement report to the base station.

According to a preferred embodiment,

-   -   the receiving means are arranged to receive a first combination        of a first and a second set of trigger conditions and the        logical function and a second combination of a first and a        second set of trigger conditions and the logical function, and    -   the checking means and the combining means are arranged to use        the first combination for radio signals from or to active base        stations having an active link with the mobile station and the        second combination is used for radio signals from or to        candidate base stations not having an active link with the        mobile station.

The measurement reporting scheme according the invention providesflexible means for reporting measurement results. The advantage of theflexibility is that the measurement reporting can be adjusted to providethe network the necessary information while minimizing the amount ofradio resources spent for the measurement reporting purposes.

The invention has been described above by means of preferred embodimentsto illustrate the principles of the invention. As regards the details,the invention may vary within the scope of the attached claims.

1. A method of measurement reporting in a telecommunication systemcomprising mobile stations and a network comprising base stations,wherein decisions upon establishing or canceling a communication linkbetween a mobile station and a base station are made in the network onthe basis of measurement reports sent from the mobile station to thenetwork, characterized in that the method comprises the steps ofdefining first and second sets of trigger conditions corresponding,respectively, to radio signal properties in the uplink and downlinkdirections, defining a logical function for combining said first andsecond sets of trigger conditions, at the mobile station, determiningthe state of each trigger condition, combining the states according tothe logical function, and sending a measurement report to a base stationin dependence upon the condition of the logical function.
 2. A methodaccording to claim 1, characterized in that the first and second set oftrigger conditions are dynamically defined by the network.
 3. A methodaccording to claim 1, characterized in that the logical function isdefined by the network.
 4. A method according to claim 1 characterizedin that a first combination of the first and second sets of triggerconditions and the logical function are defined to be used for radiosignals from or to active base stations having an active link with themobile station, and a second combination of the first and second sets oftrigger conditions and the logical function are defined to be used forradio signals from or to candidate base stations not having an activelink with the mobile station, and at the mobile station, the firstcombination is used for radio signals from or to active base stationshaving an active link with the mobile station and the second combinationis used for radio signals from or to candidate base stations not havingan active link with the mobile station.
 5. A method according to claim4, and comprising the step of creating an active link between the mobilestation and a candidate base station not having an active link with themobile station when the network receives from the mobile station ameasurement report triggered by the radio signals from or to thatcandidate base station.
 6. A method according to claim 4, and comprisingthe step of deleting an active link between the mobile station and abase station when the network receives from the mobile station ameasurement report triggered by the radio signals from or to that activebase station.
 7. A method according to claim 4, characterized in thatsaid two different logical functions are such that when a base stationis in the active set, a measurement report is not triggered by a radiosignal of that base station for the same set of radio properties aswould trigger the transmission of a measurement report when the basestation is in the candidate set.
 8. A method according to claim 1,characterized in that the method comprises a step of defining a logicalfunction for use when the number of base stations in the active set-isequal to a predefined maximum number, and defining the first and secondsets of trigger conditions is on the basis of the radio signalproperties of the active base station having the worst signalconditions, and wherein a measurement report triggered by a radio signalof a candidate base station causes that worst base station to bereplaced by the candidate base station.
 9. A method according to claim8, characterized in that the maximum number is dynamically defined bythe network.
 10. A method according to claim 1, characterized in that atleast one of the trigger conditions is a condition for the receivedpower level or a Junction thereof.
 11. A method according to claim 1characterized in that at least one of the trigger conditions is acondition for the interference in the received radio signal or afunction thereof.
 12. A method according to claim 1, characterized inthat at least one of the sets of trigger conditions is a condition forthe change of the parameters of the received radio signals or a functionthereof.
 13. A method according to claim 1, characterized in that thetrigger conditions comprise at least one base station specific offsetvalue.
 14. A method according to claim 13, characterized in that atleast one of the offset values is dynamically defined by the network.15. A method according to claim 1, characterized in that the networkinforms the mobile station what information to include in themeasurement report, and the mobile station includes this information inthe measurement report.
 16. A method according to claim 15,characterized in that the radio signals are ordered using a predefinedcondition, and in the measurement report sent from the mobile station,information about the properties of a predefined number of the bestradio signals according to the condition are reported.
 17. A methodaccording to claim 15, characterized in that the number of radio signalsto be reported is given by the network.
 18. A method according to claim15, characterized in that the measurement report comprises a value forthe path loss for a reported signal or a function thereof.
 19. A methodaccording to claim 15, characterized in that the measurement reportcomprises a value for the carrier to interference ratio of a reportedsignal of a function thereof.
 20. A method of measurement reporting in atelecommunication system comprising mobile stations and a networkcomprising base stations, wherein decisions upon establishing orcanceling a communication link between a mobile station and a basestation are made in the network on the basis of measurement reports sentfrom the mobile station to the network, the network using CDMA airinterface in which the connections are divided using different spreadingcodes, characterized in that the method comprises: defining first andsecond sets of trigger conditions corresponding, respectively, to radiosignal properties in the uplink and downlink directions, wherein atleast one of the trigger conditions is a condition for the interferencein the received radio signal or a function thereof, and wherein thevalue for the interference is an estimate for the interference powermade before the signal is correlated with the spreading code used in theconnection; defining a logical function for combining said first andsecond sets of trigger conditions, at the mobile station, determiningthe state of each trigger condition, combining the states according tothe logical function, and sending a measurement report to a base stationin dependence upon the condition of the logical function.
 21. A methodof measurement reporting in a telecommunication system comprising mobilestations and a network comprising base stations, wherein decisions uponestablishing or canceling a communication link between a mobile stationand a base station are made in the network on the basis of measurementreports sent from the mobile station to the network, the network usingCDMA air interface in which the connections are divided using differentspreading codes, characterized in that the method comprises: definingfirst and second sets of trigger conditions corresponding, respectively,to radio signal properties in the uplink and downlink directions,wherein at least one of the trigger conditions is a condition for theinterference in the received radio signal or a function thereof, andwherein the value for the interference is an estimate for theinterference power made after the signal is correlated with thespreading code used in the connection; defining a logical function forcombining said first and second sets of trigger conditions, at themobile station, determining the state of each trigger condition,combining the states according to the logical function, and sending ameasurement report to a base station in dependence upon the condition ofthe logical function.
 22. A mobile station for a telecommunicationsystem comprising mobile stations and a network comprising basestations, wherein the mobile stations monitor the radio signals sent bythe base stations, characterized in that the mobile station hasreceiving means for receiving information about first and second set oftrigger conditions corresponding, respectively, to uplink and downlinksignals and a logical function, monitoring means for monitoring radiosignals, checking means which is responsive to the receiving means andthe monitoring means and which has the functionality of checking thestate of each trigger conditions, combining means responsive to thechecking means for combining the states according to the logicalfunction, and sending means responsive to the combining means forsending a measurement report to the base station.
 23. A mobile stationaccording to claim 22 characterized in that the receiving means arearranged to receive a first combination of a first and a second set oftrigger conditions and the logical function and a second combination ofa first and a second set of trigger conditions and the logical function,and the checking means and the combining means are arranged to use thefirst combination for radio signals from or to active base stationshaving an active link with the mobile station and the second combinationis used for radio signals from or to candidate base stations not havingan active link with the mobile station.
 24. A base station for atelecommunication system comprising mobile stations and a networkcomprising base stations, wherein the base stations send radio signalsmonitored by the mobile stations, the base station comprising: a firstdefining means for defining first and second sets of trigger conditionscorresponding, respectively, to radio signal properties in uplink anddownlink directions, and a second defining means for defining a logicalfunction for combining said first and second sets of trigger conditions.25. The base station according to claim 24, wherein the base stationfurther comprises: transmitting means for transmitting the defined firstand second sets of trigger conditions and the defined logical functionto at least one mobile station.
 26. The base station according to claim25, wherein the base station further comprises: measurement reportreceiving means for receiving a measurement report from a mobilestation, the measurement report having been prepared by said mobilestation on the basis of states of the first and second sets of triggerconditions and the logical function transmitted to said mobile station.